EMC3 is critical for CFTR function and calcium mobilization in the mouse intestinal epithelium

Membrane proteins, such as the cystic fibrosis transmembrane-conductance regulator (CFTR), play a crucial role in gastrointestinal functions and health. Endoplasmic reticulum (ER) membrane protein complex (EMC), a multi-subunit insertase, mediates the incorporation of membrane segments into lipid bilayers during protein synthesis. Whether EMC regulates membrane proteins' processing and function in intestinal epithelial cells remains unclear. To investigate the role of EMC in the intestinal epithelium, we generated mice in which EMC subunit 3 (EMC3) was deleted in intestinal epithelial cells (EMC3^ΔIEC). EMC3^ΔIEC mice were viable but notably smaller compared with their wild-type littermates. Although the intestinal structure was generally maintained, EMC3^ΔIEC crypts exhibited altered morphology, particularly at the base of the crypts with decreased goblet cells and paneth cells. Levels of multiple polytopic membrane proteins, including CFTR, were decreased in EMC3-deficient epithelial cells. Several calcium ATPase pumps were downregulated, and calcium mobilization was impaired in EMC3^ΔIEC enteroids. CFTR-mediated organoid swelling in EMC3^ΔIEC mice was impaired in response to both cAMP-dependent signaling and calcium-secretagogue stimulation. Our study demonstrated that EMC plays a critical role in maintaining intestinal epithelium homeostasis by regulating membrane protein biogenesis and intracellular calcium homeostasis. Maintaining intracellular calcium homeostasis may be a universal cellular function regulated by EMC.<b>NEW & NOTEWORTHY</b> We generated mice in which endoplasmic reticulum membrane protein complex (EMC) subunit 3 was deleted from intestinal epithelium cells and studied the molecular functions of EMC in vivo. Our findings demonstrate the importance of intestinal EMC in the biogenesis of membrane proteins in vivo, including CFTR, and highlight its critical role in maintaining intracellular calcium homeostasis and, consequently, in calcium-dependent functions in the intestine and beyond.